In a discovery that surprised even the scientists who made it, scientists have unravelled what really happens, when we make and store memories.

In a discovery that surprised even the scientists who made it, scientists have unravelled what really happens, when we make and store memories.
The US and Japanese team found that the brain "doubles up" by simultaneously making two memories of events.
One is for the here-and-now and the other for a lifetime, they found.

It had been thought that all memories start as a short-term memory and are then slowly converted into a long-term one.
Experts said the findings were surprising, but also beautiful and convincing.

Two parts of the brain are heavily involved in remembering our personal experiences.
The hippocampus is the place for short-term memories while the cortex is home to long-term memories.

This idea became famous after the case of Henry Molaison in the 1950s.
His hippocampus was damaged during epilepsy surgery and he was no longer able to make new memories, but his ones from before the operation were still there.
So the prevailing idea was that memories are formed in the hippocampus and then moved to the cortex where they are "banked".

The team at the Riken-MIT Center for Neural Circuit Genetics have done something mind-bogglingly advanced to show this is not the case.
The experiments had to be performed on mice, but are thought to apply to human brains too.

They involved watching specific memories form as a cluster of connected brain cells in reaction to a shock.
Researchers then used light beamed into the brain to control the activity of individual neurons - they could literally switch memories on or off.

The results, published in the journal Science , showed that memories were formed simultaneously in the hippocampus and the cortex.

The researchers also showed the long-term memory never matured if the connection between the hippocampus and the cortex was blocked.
So there is still a link between the two parts of the brain, with the balance of power shifting from the hippocampus to the cortex over time.
Dr Amy Milton, who researches memory at Cambridge University, described the study as "beautiful, elegant and extremely impressive".